1. Field of the Invention
The present invention relates to a fibroin fluid for use as a main ingredient or an additive in the fields of pharmaceuticals, cosmetics, hygiene or foods.
2. Description of the Related Art
As far as fibroin is concerned, a fibroin in a gel state is known. The fibroin in a gel state is obtained by adding an acid such as citric acid or acetic acid to silk protein to decrease its pH to an isoelectric point, or by adding sericin or other polysaccharide as a gelating agent.
A fibroin in a gel state ("fibroin gel" hereinafter) has a network structure in its entire system so that it is of one mass as a whole gel, and as a result, it cannot be brought into a "cream" state. Further, the fibroin gel is poor in water retention, and when the gel is allowed to stand, it cracks since contained water is lost.
On the other hand, when a fibroin gel is prepared by adding an additive such as citric acid or the like, it is difficult to remove the additive after the gelation, and the residual additive as an impurity in the gel has an adverse effect on the quality of an end product obtained from the fibroin gel. Moreover, the added gelating agent such as citric acid or other acids is not only present as an impurity, but it works on the crosslinked structure of fibroin to prevent the fibroin gel from exhibiting the adsorption capacity inherent to the fibroin gel.
As described above, fibroin gel has physical problems that it cannot be brought into a cream state and is poor in water retention, and it also has a production-wise problem that it contains an additive which causes a poor product quality. Therefore, although fibroin itself has a potential for its wide applications in the fields of pharmaceuticals, foods and cosmetics, these applications of the fibroin gel are impossible, and the use of fibroin is limited to very narrow fields.